1. Field of the Invention
This invention relates to a bearing unit which supports a rotary shaft for rotation thereon or supports a rotatable member for rotation on a shaft, and a motor and an electronic apparatus which have a bearing unit.
2. Description of the Related Art
Various bearing units for supporting a rotary shaft for rotation thereon are known in the past, and an exemplary one of such bearing units is disclosed in Japanese Patent Laid-Open No. 2005-147265 and is shown in FIG. 10.
Referring to FIG. 10, the bearing unit 100 shown supports a rotary shaft 101 for rotation thereon and includes a radial bearing 104 for supporting the rotary shaft 101 in a circumferential direction and a housing 105 which accommodates the radial bearing 104 therein.
In the bearing unit 100, the radial bearing 104 cooperates with lubricating oil as viscous fluid filled in the housing 105 to form a dynamic fluid bearing. Dynamic pressure generating grooves 111 for generating a dynamic pressure are formed on an inner circumferential face of the radial bearing 104 in which the rotary shaft 101 is fitted.
The housing 105 in which the radial bearing 104 which supports the rotary shaft 101 is accommodated is one member which is formed by integral molding of a synthetic resin material and has such a shape that it accommodates and surrounds the radial bearing 104 formed in a cylindrical shape as seen in FIG. 10.
The housing 105 includes a cylindrical housing body 106, and a bottom closing portion 107 formed integrally with the housing body 106 in such a manner as to close up one end side of the housing body 106 and forming a one-end side portion. An upper closing member 108 is provided on the other end side of the housing body 106 which is open. The housing 105 and the upper closing member 108 are integrated with each other using such a technique as heat sealing or ultrasonic sealing.
The upper closing member 108 has a shaft fitting hole 109 formed at a central portion thereof. The rotary shaft 101 supported for rotation on the radial bearing 104 accommodated in the housing 105 is fitted in the shaft fitting hole 109.
The shaft fitting hole 109 is formed with an inner diameter a little greater than the outer profile of a shaft body 103 so that the rotary shaft 101 fitted in the shaft fitting hole 109 may rotate without slidably contacting with an inner circumferential face of the shaft fitting hole 109. The shaft fitting hole 109 is formed such that an air gap 112 of a distance sufficient to prevent leakage of lubricating oil 113 filled in the housing 105 from within the housing 105 is formed between an inner circumferential face of the shaft fitting hole 109 and an outer circumferential face of the shaft body 103.
Further, a thrust bearing 110 is formed integrally at a central portion of the inner face side of the bottom closing portion 107. The thrust bearing 110 supports a bearing support portion 102, which is provided at the one end portion in a thrust direction of the rotary shaft 101 supported on the radial bearing 104, for rotation thereon.
The thrust bearing 110 is formed as a pivot bearing for supporting the bearing support portion 102, which is formed in an arcuate shape or in a tapering shape, of the rotary shaft 101 at a point.
A coming out preventing member 115 in the form of a washer or the like is provided between the bearing support portion 102 and the shaft body 103. The coming out preventing member 115 has an inner diametrical dimension smaller than the dimension of an outer diameter of the rotary shaft 101 and is disposed in a grooved portion 116 provided at an end portion of the rotary shaft 101. When the rotary shaft 101 is moved in a coming out direction, a lower edge of the grooved portion 116 of the rotary shaft 101 is contacted and interferes with the coming out preventing member 115 so that the rotary shaft 101 is prevented from coming out and dropping from the housing 105 by the coming out preventing member 115.
A gap Y3 for preventing the coming out preventing member 115 from disturbing rotation of the rotary shaft 101 is provided between an outer circumference of the grooved portion 116 of the rotary shaft 101 and an inner circumference of the coming out preventing member 115. Meanwhile, another gap X4 is provided between an end face which defines the lower edge of the grooved portion 116 and a bottom face of the coming out preventing member 115, and a further gap X5 is provided between an end face which defines an upper edge of the grooved portion 116 and an upper face of the coming out preventing member 115.
The bearing unit 100 having such a configuration as described above with reference to FIG. 10 can prevent the rotary shaft 101 from coming out from the housing 105 by means of the coming out preventing member 115 configured in such a manner as described above.
Incidentally, for example, a rotor assembly not shown is attached to an upper portion of the rotary shaft 101. Thus, when the rotary shaft 101 moves in the coming out direction, the weight of the rotor assembly acts as a load upon the coming out preventing member 115. Particularly when an impact is applied, since an increased load of several tens times the load of the rotor assembly is applied to the coming out preventing member 115, high strength is demanded for the coming out preventing member 115 described above. In other words, strength sufficient to prevent the rotary shaft 101 from coming out is demanded for the coming out preventing member 115. Such strength is hereinafter referred to as coming out preventing force.
As a countermeasure for increasing the coming out preventing force, that is, the coming out withstanding force, of the coming out preventing member 115, a method of increasing the thickness of the coming out preventing member 115 in the axial direction, another method of decreasing the inner diametrical dimension of the coming out preventing member 115 to increase the contact area between the coming out preventing member 115 and the grooved portion 116 of the rotary shaft 101 to increase the meshing engagement between them and a like method seem applicable. However, since the coming out preventing member 115 is attached to the grooved portion 116 of the rotary shaft 101 such that the coming out preventing member 115 is resiliently deformed into an umbrella shape and inserted into and attached to the grooved portion 116, whereupon the coming out preventing member 115 restores its original shape, where the coming out preventing force or coming out resisting force is increased by any of such methods as described above, it is necessary to increase the gap X4 between the lower edge of the grooved portion 116 and the coming out preventing member 115. Then, if the gap X4 is not provided with a necessary dimension, then the coming out preventing member 115 is placed into and remains in a state wherein it is caught by an end portion of the rotary shaft 101 and deteriorates the rotational performance of the rotary shaft 101, resulting in the possibility that such a problem that the rotary shaft 101 does not rotate or rotates but abnormally may occur. On the other hand, increase of the size of the gap X4 may cause another problem that the dimension of the bearing unit 100 in the axial direction increases or that the rotary shaft 101 floats in the coming out direction to allow air to be admitted into the lubricating oil 113.
Also a method of selecting a metal material having a high breaking strength as the material of the coming out preventing member 115 in order to increase the coming out preventing force or coming out withstanding force of the coming out preventing member 115 seems applicable. However, when the coming out preventing member 115 is attached to the rotary shaft 101, there is the possibility that plastic deformation may occur with the coming out preventing member 115, resulting in a problem that the rotational performance of the rotary shaft 101 is damaged similarly.